Visitor interaction with networked resources is often tracked using client tracking identifiers such as cookies. For a variety of reasons, tracking identifiers such as cookies may be rejected, deleted or corrupted over time. As a result, first and/or third party servers may serve new cookies with new cookie values to client systems. Over time, multiple cookie values may become associated with each visitor, visitor entity and/or client, complicating first party and/or third party tracking. For example, a first party and/or third party server may maintain a database of cookie values associated with a visitor entity based at least in part on a server-side history of first and/or third party cookie setting activities. These databases can grow very large, becoming slow and cumbersome to operate and maintain.
The number of client tracking identifiers associated with each visitor, visitor entity and/or client may be reduced by attempting to synchronize first and third party cookie values. However, security policies associated with many common browsers make synchronizing cookie values somewhat complicated. Security policies govern how client tracking identifiers such as cookies may be created, viewed, set and/or re-set. For example, a “same origin” security policy is intended to prevent the direct manipulation or access of cookies originating from a first origin by a document or script from another origin. For example, under such a security policy, a website publisher's cookie (a first party cookie) resident on a client system may not be directly read or altered by an analytics server (a third party server) which is external to the website publisher's security domain. Under a “same origin” security policy, cookie synchronization may require communication-intensive techniques which may introduce delays and consume server resources. Synchronization of other types of client tracking identifiers may be complicated by analogous difficulties. What is needed is a method for synchronizing client tracking identifiers from multiple security domains.